Depending on the nature of a sprinkler system and the environment it is designed to protect, the system valve may be any of the following types: alarm valve ("wet" system), deluge valve ("wet" or "dry" systems), check valve (one-way valve), dry valve ("dry" system), dry differential valve ("dry" system), gate valve and butterfly valve. The present invention is directed to a clapper seal for a dry valve.
The model "H" dry pipe valve manufactured by Central Sprinkler Corporation has a clapper differential of approximately six to one. By clapper differential is meant the ratio of air seal area to water seal area. When the system air pressure drops to approximately 1/6 the water pressure at the inlet port, then, the water supply pressure lifts the clapper valve. When the clapper valve lifts, it allows water to flow into the sprinkler system piping. Details of the model "H" dry pipe valve are available in Central Sprinkler Corporation bulletin DPV-H-4-6 (Rev. No. 2).
Conventionally, the clapper valve is sealed by an annular gasket or facing, made of resilient rubber. The gasket is secured to the clapper valve by a rigid, annular metallic washer or plate and a plurality of retaining bolts. The gasket radially bridges an annular gap between an air ring and a water ring located inside the valve housing. The air ring and water ring are cylindrical sleeves which separate the water and air sides of the valve. The metallic washer is disposed within the annular gap between the air ring and water ring. The clapper valve body is provided with a centering hub which plugs the water ring.
Under certain system conditions, the conventional seal design permits water penetration or seepage from the water supply side (inside the water ring) to the air or sprinkler system side (outside the air ring). Seepage tends to occur around the centering hub, at the central opening of the rubber gasket, and across the interface between the clapper valve body and rubber gasket. The seepage rate is low so that the condition may not be sensed by (built-in) valve detector switches. Water seeping through the seal tends to "column" or flow upwards into the sprinkler system piping. Since "dry" systems are normally required in areas subject to freezing conditions, this undetected water seepage poses serious problems, namely, danger of pipe freeze-up and catastrophic rupture. As an example of the potential severity of the problem, a six inch diameter pipe, at 100 psi water pressure, could dump approximately 800 pounds of water per minute if fully fractured.
A further shortcoming of the conventional seal design is long-term deformation of the rubber gasket at the zones of contact with the air and water rings. Most sprinkler systems encounter pressure surges on the water supply side. The rubber gasket, due to its pliable nature, is therefore subjected to compressive forces of varying magnitudes. The peripheral edge portions of the rubber gasket, at the contact areas with the air and water rings are subjected to over-compression or long-term compressive set. These portions of the rubber gasket tend to become over-stressed and brittle, and they may eventually fail.
The present invention is directed to a solution to the foregoing problems. The invention is a clapper seal for a dry pipe valve wherein over-compression or long-term compressive set of the sealing gasket is limited at the areas of contact with the air and water rings and wherein water seepage and excessive deformation of the sealing gasket are essentially eliminated. The water ring is capped by a disc-shaped sealing gasket so that water seepage at the interface between the clapper valve body and the gasket is impossible.